1. Field of the Invention
The invention relates in general to a switching power converter, and more particularly to an efficiency-enhancing switching power converter.
2. Description of the Related Art
Switching power converter, which is for rectifying an AC power and then outputting a DC power, is widely applied in electronic devices. FIG. 1 is a circuit diagram of conventional switching power converter 100. Switching power converter 100 includes a transformer, resistors R1, R2, R3, R4, R5, R7, R8 and R14, diodes D2, D3 and D14, capacitors C1, C3 and C22, an inductor L5, and a transistor M1. The transformer includes a primary side coil L1 and a secondary side coil L3. The switching power converter 100 rectifies a power Vb+ according to control signal Vin and outputs a DC power Vo. The diode D14 is electrically connected to the secondary side coil L3 for rectifying.
Considering worldwide energy specification and consumers' demands, energy saving and power efficiency enhancing have become urgent goals for the manufacturers of electronic devices to achieve. Besides, if power consumption can be reduced, temperature of electronic device will be reduced as well.
However, when the diode D14 is used to rectify, the efficiency of the switching power converter 100 cannot be good. Given that the output voltage Vo is 3.3V and that the diode D14 is a Schotty diode, the forward voltage of the diode D14 is 0.7V, and the efficiency of switching power converter 100 is 3.3/(3.3+0.7)=82.5%. Given that the output voltage Vo is 12V and that the diode D14 is an ultra-fast diode, the forward voltage of the diode D14 is 0.95V, and the efficiency of the switching power converter 100 is 12/(12+0.95)=92%.